The present invention relates to exercising apparatus of the weight lifting type. These types of devices are well known in the art and typically employ such means as one or more weight plates which are lifted by means of a lifting bar. They are commonly referred to as dumb-bells, bar bells, and/or free weights. As used herein, all three terms shall be deemed equivalent.
The present invention is more specifically related to variable resistance exercise devices which compensate for changes in body leverage during an exercise movement. Such leverage changes are caused by the lever effect that a straight line muscle contraction has upon a body part that rotates about a joint.
One limitation associated with the use of barbells as been the loss in resistance that is encountered as the weight approaches a point directly over or under the axis of rotation. In a bicep curl, for example, the substantial portion of the weight is borne by the skeletal structure when the weight is over the elbow. As the curl movement is continued toward the body, the weight actually pulls the arm in the direction of travel.
The search for an exercise device which provides a relatively constant resistance throughout the exercise movement has been substantial. Owing to both leverage changes during the movement, and to the loss in resistance as the weight approaches the aforedescribed position, those skilled in the art have assumed that the barbell has inherently limited utility.
Accordingly, there has been an emphasis recently on expensive and complex equipment utilizing cams or fluid pressure to provide relatively constant resistance and a "smooth" feeling to facilitates maximum stressing of the muscle throughout the exercise movement. However, such equipment has its own limitations in that they work the major muscle groups but ignore the minor muscle groups by restricting movement to a pre-defined arc and eliminating the need to balance the weights during the exercise movement. Additionally, the pre-defined arc may not match the natural movement of the user.
U.S. Pat. No. 4,231,569 discloses an exercising frame having one end portion which is gripped by the user, a second end portion longitudinally spaced from the first end along a longitudinally extending frame axis and to which a pair of weights are attached, and an intermediate portion therebetween. A handle is rotatably attached to said forst end for rotation of the frame about an axis which is transverse to the frame axis. The intermediate portion contains an arm-engaging surface which keeps the weight from reaching a point above the elbow during the curling movement.
While the device disclosed in the forgoing patent provides resistance througout a curling movement, it does not compensate for changes in body leverage. Additionally, it represents an extra piece of equipment.